1. Field of the Invention
The present invention relates to a method and a system for monitoring a cable system of an electric power transmission system.
2. Description of the Related Art
Electric power transmission from a power generating plant is typically performed by means of high voltage electric power transmission systems that may be aerial (overhead), terrestrial or submarine.
An electric power transmission system typically comprises electric conductors either aerial (overhead), terrestrial or submarine - junctions and terminations.
It is advantageous to monitor various parameters of an electric power transmission system, such as temperature, partial discharges, pressure, voltage, current, etc., during the system operation so that a failure can be detected and located soon after occurrence, or, even better, to try and foresee a possible failure and to schedule the suitable in situ checking.
WO 99/58992, for example, discloses a power cable monitoring system comprising one or more transducers distributed along a sea cable. Each of the transducers is operationally connected to the sea cable for measurement of operational parameters of the sea cable, such as temperature, pressure, voltage, current, etc., and provides an output signal in response to actual parameter values. A data cable extends substantially in parallel with the sea cable. The data cable is operationally connected to the transducers via corresponding branching units, for transmission of output signal to a controller.
WO 99/58992 states that in the power cable monitoring system wherein the transducers and associated electronic circuits receive their power supply from batteries, considerable power savings may be obtained by designing the electronic circuits to operate in a power down mode and in an active mode. In the power down mode, the circuits are in an idle mode and no data is transmitted to the data cable, and in the active mode transducer parameter values are converted into data signals for transmission through the data cable. Operation of the circuits may be controlled by means of a timer circuit comprised in the transducer signal converter. The timer may be programmed to interrogate the transducer signal converter at predetermined time intervals. Upon timer interrogation, the transducer signal converter changes operation mode from its power down mode to its active mode. In the active operation mode, the transducer output signal is converted into a data signal and the data signal is transmitted to the controller. The transducer signal converter returns to its power down mode after the data signal has been transmitted.